The invention relates to a gripper device for a tufting machine, in particular for the manufacture of carpets with cut pile.
Frequently, tufting processes are used in the manufacture of carpets. Referring to such tufting methods, a flat support material (so-called backing) is provided with a pile. The pile consists of a large number of individual pieces of yarn which are punched by tufting needles—row by row—into the backing. In so doing, the backing is gradually advanced stitch by stitch underneath a row of needles. The thusly formed loops are temporarily held by a gripper arranged on the opposite side and are cut by means of a knife, consistent with the advance cycle of the backing. Consequently, a cut pile is obtained, which is also referred to as velour.
In so doing, the gripper device interacts with the tufting needles, on the one hand, and with the knives, on the other hand. When the loops are picked up, the grippers' tips contact the tufting needles. As a result of the relatively high contact pressure exerted by the knives on the grippers, the grippers are pressed against the needles. As a result, the needles wear out relatively rapidly. Therefore, the gripper tip should not be too hard, yet still exhibit good wear characteristics.
In addition, the cutting edges and the cutting surfaces on the gripper devices wear out relatively rapidly due to the frictional contact with the knife during the shearing movement. The knives move with high pressure and diagonally across the cutting edges of the gripper devices, thus requiring high edge strength and high hardness of the gripper devices.
In practical applications it has been known to make the grippers of high-speed steel (HSS). However, such grippers result in a rapid wear of the needles. Furthermore, known practical applications have shown grippers consisting of relatively soft material; such grippers are provided with hard metal inserts for the blade, said inserts being soldered or cemented in place. The adjustment of such grippers on the tufting machine is difficult. Furthermore, the precise material properties of the gripper body can be affected by thermal stress when the hard metal blades are soldered in, or the gripper body can be distorted. It is difficult to maintain the desired precision. In addition, hairline cracks may occur in the hard metal bodies.
If, in contrast, the grippers consist of only one uniform material, a compromise can hardly be found regarding the wear characteristics during the interaction with the tufting needle, on the one hand, and regarding the interaction with the knife, on the other hand.
Considering this, it is the object of the invention to improve the gripper device.